Radon (222Rn) gas is the largest source of public exposure to naturally
occurring radioactivity and the identification of radon priority areas is
required by the Council Directive 2013/59/Euratom. Radon is also used as a
tracer to improve atmospheric transport models and to indirectly estimate
greenhouse gas (GHG) fluxes using the Radon Tracer Method (RTM). This method
is based on the correlation between atmospheric concentrations of radon and
GHG, together with information on the radon flux data. For radiological
data, all European countries have installed networks of automatic gamma dose
rate monitoring stations and report the real-time information gathered to
the European Radiological Data Exchange Platform (EURDEP). So far,
atmospheric radon activity concentrations and radon fluxes are not yet
reported in EURDEP, nor routinely measured within the European radiological
networks although these observations could help to avoid false positives
results.
Due to above applications, there is a need of building a metrological chain
to ensure high quality radon activity concentrations and radon flux
measurements. Both climate and radiation protection research communities
underline the need for improved traceability in low-level atmospheric radon
measurements (Khanbabaee et al., 2021). The EMPIR project 19ENV01
traceRadon
This project 19ENV01 traceRadon has received funding
from the EMPIR programme co-financed by the Participating States and from
the European Union's Horizon 2020 research and innovation programme. 19ENV01
traceRadon denotes the EMPIR project reference.
is aimed towards
providing the necessary measurement infrastructure and transfer standards to
fulfil this need.
Results of this project are particularly important for improving independent
GHG emission estimates that support national reporting under the Paris
Agreement on climate change and for the Council Directive 2013/59/Euratom,
thus benefitting two large scientific communities. In this paper, early
results, such as new activity standard developments and an overview of
commercial and research radon monitors are presented and discussed. These
results will feed into the traceRadon project with respect to radionuclide
metrology in air and its potential for the improvement of the RTM.
Introduction
The radioactive noble gas radon is a health hazard when accumulated indoor,
from a radiation protection point of view. However, radon is being also
studied in the environment as a useful tracer to investigate atmospheric
processes, to improve Atmospheric Transport Models (ATM) or indirectly
retrieve fluxes of greenhouse gases. To increase the comparability for both
radiation protection measurements as well as those used for GHG modelling,
traceability to the SI is needed for radon release rates from soil as well
as its concentration in the atmosphere. Radon flux relates to the transfer
process of radon activity from soil to the atmosphere per square meter and
second (Bq m-2 s-1), whilst radon activity
concentration is the amount of activity of radon in the atmosphere per cubic
meter (Bq m-3). Traceability to a primary standard does not
currently exist for these quantities, which limits the usability of their
measurements and their harmonization across Europe.
Climatic Atmospheric Monitoring Networks (AMN) like the pan-European
Integrated Carbon Observation System (ICOS, http://www.icos-cp.eu, last access: 2 March 2022), are
infrastructures that operate GHG monitoring stations and are also including
atmospheric radon measurements based on different techniques
(Schmithüsen et al., 2017; Grossi et al., 2020). The radon data from
these networks can be used, among others, to improve ATM, to study
atmospheric processes and to indirectly estimate GHG fluxes by the Radon
Tracer Method (RTM) (e.g., Van Der Laan et al., 2010; Levin et al., 2011, 2021;
Vogel et al., 2012; Wada et al., 2013; Grossi et al., 2014,
2018), which uses the correlation between GHG and radon
activity concentrations assuming a known radon flux over the footprint area.
These measurements need significant improvement in terms of the accuracy of
the environmental radon activity concentrations which ranges usually between
1 and 100 Bq m-3 to be able to
provide robust data for the use in the RTM and thus minimize the
uncertainties on the retrieved GHG fluxes. At present, commercial radon
monitors currently available on the market present a high uncertainty when
measuring radon activity concentration below 100 Bq m-3 as
reported by Radulescu et al. (2022). Radon flux data, useful to validate
radon flux maps and models, also need a robust traceability chain and a
related infrastructure as explained in detail by Röttger et al. (2021).
Similarly, for radiation monitoring, all European countries have installed
networks of automatic radiation dose and airborne contamination monitoring
stations and report the information gathered to the EURDEP, thus supporting
EU member states and the EURATOM treaty (Sangiorgi et al., 2020). Currently,
monitoring information on dose rates is collected from 5500 automatic
surveillance systems in 40 countries, however, urgently needed data on
outdoor (atmospheric) radon activity concentrations is not yet collected due
to a lack of harmonization between research monitors able to measure
accurately at the low levels encountered in the environment. Furthermore,
accurately detecting radioactivity from nuclear and radiological emergencies
using ambient dose rate measurements relies on rejecting false positive
results based on particulate radon progeny washed from the atmosphere by
rain. Therefore, improving early warning detection systems for radioactivity
requires greater accuracy in determining environmental radon activity
concentrations.
Project plan of traceRadon
The project traceRadon, started in June 2020 joining together the
atmosphere, climate and the environmental radiation scientific communities
under the umbrella of EURAMET, the European Association of National
Metrology Institutes. At the very moment 18 partners and 12 collaborators
are working towards a European harmonisation within the goals of this
project, which consists of four technical Working Packages (WP):
WP1 aims to develop traceable methods for the measurement of outdoor
low-level radon activity concentrations in the range of 1 to 100 Bq m-3 with uncertainties of 10 %
(k=1) to be used in climate and radiation protection networks. These
methods will include two new traceable 222Rn emanation sources below
100 Bq m-3, a traceable transfer instrument calibrated with
these new sources and a calibration procedure suitable to enable a traceable
calibration of environmental atmospheric radon measurement systems in the
field;
WP2 aims to improve the accuracy of radon flux measurements for the purpose
of: (1) identifying Radon Priority Areas (RPAs) for radiation protection
goals; and (2) retrieving indirect GHG fluxes using the RTM. Within this work
package four experimental measurement campaigns will be carried out at
different European stations in order to produce high quality data to
validate available radon flux models (Karstens et al., 2015) and inventories
(Szegvary et al., 2009);
WP3 aims to validate current radon flux models and inventories using
traceable measurements of radon flux and radon activity concentration
supported by dosimetric and spectrometric data from the radiological early
warning networks in Europe and, in addition, to improve process-based radon
flux maps that can be used in the RTM, ATM and radiation protection;
WP4 will provide dynamic outdoor radon concentration and radon flux maps for
climate change research and radiation protection. These last maps will be
provided through the Radioactive Environmental Monitoring web portal (REMon,
https://remon.jrc.ec.europa.eu, last access: 2 March 2022) operated by the
Joint Research Centre of the European Commission and through the ICOS Carbon
Portal (https://www.icos-cp.eu, last access: 2 March 2022). This new data will
be linked to established data from EURDEP and EANR (https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation/Digital-Atlas, last access: 2 March 2022, Cinelli et al., 2019) and will be made available to scientists, policy
makers and end users.
The project plan is laid out for 3 years and the work in the working
packages is being performed in parallel. The project is managed by a
coordinator and its results are disseminated by a dedicated impact work
package. A social media account (@traceradon) is sharing the project news on
a daily basis.
Motivation for the need of traceability
In the context of Earth system research, more detailed investigations of
exchange processes of fluxes of GHG have increasingly come into focus in
recent decades. Continuous measurements of GHG fluxes (CO2, CH4,
N2O) between different ecosystems and the atmosphere are extremely
heterogeneous because they are mainly dominated by local-scale changes in
their sources and sinks, chemical reactions, as well as meteorological
conditions. Local GHG flux measurements on the meter to kilometre scale are
therefore often not representative of regional exchange rates on the scale
of several kilometres. Here, the naturally occurring noble gas radon, which
is emitted from continental soils but not from water bodies (such as oceans,
seas, lakes, etc.) can help to overcome these difficulties by using it as a
tracer for boundary layer mixing processes.
Similar to other gases which have distributed sources close to the ground
radon accumulates, is mixed, and disperses within the atmospheric boundary
layer. If the radon flux from the soil is known, the correlated increase of
radon and GHG concentration can be used to estimate the GHG flux. Radon
emissions from the land surface are influenced by the geophysical properties
of the soils and its only sink is its radioactive decay (T1/2≈3.8 d). Radon is produced continuously by radioactive decay of radium
(226Ra) in the soil, but its exhalation rate to the atmosphere is
influenced by geophysical propriety of the soils (porosity, permeability,
etc.) and by climatic conditions (rain, snow, temperature, etc.) (López-Coto
et al., 2013; Karstens et al., 2015). Compared to the large spatiotemporal
heterogeneity of GHG fluxes, radon emissions from ice-free land are often
assumed to be more homogeneous (or at least uncorrelated with changes in the
GHG fluxes on local spatial scales and diurnal time scales) and therefore
easier to model. However, the reliability of the GHG flux estimates depend
critically on the accuracy and representativeness of the value used for the
radon flux in the footprint of the measurement station (Grossi et al., 2018;
Levin et al., 2021) and hence requires a careful validation of the radon
flux maps. Similarly, regional atmospheric transport models, such as those
used in weather forecasting, can be validated and/or improved using radon as
a transport tracer (e. g. Olivié et al., 2004; Koffi et al., 2016).
Within traceRadon, new chains of traceability are developed with respect to
the activity concentration in the atmosphere as well as for the radon flux
from the soil. Traceability in the metrological sense means that the
measurement procedure is linked to the SI system of units in an absolute
sense, in the expected measurement range (Röttger and Honig, 2011). An
important part of the calibration and the measurement is the assignment of
an uncertainty, which includes all individual uncertainty contributions
(statistics of the measurement, uncertainty of the calibration, intrinsic
background of the instrument, etc.). Because radon is so well suited as a
tracer for climate monitoring, very sensitive radon monitors have been
developed for this purpose during the last years by research entities and
are running at different European atmospheric stations (Whittlestone and
Zahorowski, 1998; Levin et al., 2002; Grossi et al., 2012; Griffiths et al.,
2016). Sensitive means that, even at small activity concentrations down to
few Bq m-3, small changes can be observed on an hourly
basis. The ability to observe relative changes with a small uncertainty,
however, says nothing about the uncertainty of the absolute value. The lack
of traceability so far prevents radon measurements from being compared
independently of the devices used at the different AMN stations as well as
at radiological stations. Since the measuring devices are usually
permanently installed at one location, the aim of the project is to develop
a transportable calibration option for them.
The traceability for radon flux will not be covered by this publication in
detail. But currently it can be stated that based on the observed needs, a
radon “exhalation bed” to be used as a calibration facility has been
designed and constructed. Several experiments were carried out with the aim
for testing the reliability of an exhalation bed and to calibrate radon flux
systems under different environmental conditions. Up to now different radon
flux systems were simultaneously tested over the bed surface under dynamic
or static conditions. The evaluation is not finished but shows promising
results.
The need for a protocol for the application of the Radon Tracer Method (RTM)
Atmospheric radon measurements are used in numerous atmospheric studies due
to radon's unique physical and chemical characteristics (e.g., inert gas,
simple source, and only radioactive decay as a sink). Among these
applications, radon measurements in combination with GHG measurements can be
used to indirectly estimate emission fluxes using the RTM (Dörr et al.,
1983). The RTM uses atmospheric measurements of radon and the GHG of
interest and measured, or modelled, values of radon fluxes. The RTM is based
on the assumption that the nocturnal lower atmospheric boundary layer can be
described as a well-mixed box of air where the changes in the radon and GHG
concentrations are only due to their respective fluxes' contribution into
the atmospheric volume. The change in atmospheric concentration conditions
can be described as:
ΔCiΔt=∫t0t1h(t)-1jidt=h-1‾ji‾
Where h(t) is the time dependent mixing height, ji(t) represents the
surface flux of a species i, and ΔCi is the departure of its
concentration relative to initial background levels for a given observation
time Δti.e.t1-t0 The overbar indicates
that both mixing height and net surface flux of the catchment area are
averaged for the observation period. This version of the box model assumes a
constant h-1 over the time window and neglects the radioactive decay of
radon over the integration time period. Since the Eq. (1) can be obtained for both gases (e.g., 222Rn
and GHG), the mixing layer height (which may be unknown) and time step
cancel after taking the ratio yielding:
jx‾=ΔCxΔC222RnjC222Rn‾
Where ΔCx and ΔC222Rn represent the
concentration enhancements of species x (in this case one of the GHG) and
radon above their respective background levels for a given observation
period. The jx‾ and jC222Rn‾ represent
the mean surface fluxes of 222Rn and GHG of the sources within the
catchment footprint.
Radon flux, used for RTM applications in the literature, was usually taken
as a constant value obtained by experimental measurements carried out close
to the atmospheric station where radon and GHG atmospheric measurements were
obtained or from the output of radon flux models in the grid containing the
station location. Grossi et al. (2018) proposed for the first time to use
within the RTM a potentially different “effective” radon flux influencing
the atmospheric station each night of the studied time series. This value,
changing for each night episode, was calculated by coupling the radon flux
model, with the resident time map of the air masses over the region of
interest. This last map was calculated using the backtrajectories with an
atmospheric transport model (in their case the ECMWF-FLEXPART model (version
9.02) (Stohl et al., 1998)). This new methodology also accounts for the spatial
variability of the radon flux within the footprint of the station which
could be a significant problem for the RTM application as reported by Levin
et al. (2021).
RTM is therefore based on both radon and GHG atmospheric concentration time
series. However, so far RTM applications studies were carried out using: (1)
local radon activity concentrations measured with different techniques and
without being supported by a robust metrological traceability chain; (2)
using radon flux value from not validated radon flux models or from
experimental observations not supported by a proper petrology; (3) individual
RTM without a specific application protocol. Thus, so far, GHG fluxes
obtained by RTM at different locations and by different scientists cannot be
compared because the RTM has not yet a unique application protocol. Firstly,
there is a need to develop a traceability chain for radon instrument
calibration from lab to field and secondly a standard protocol for RTM
application is required where it should be specified, among others, the
length of the nocturnal window to be analysed, the threshold of the linear
correlation between radon and GHG during their increase, how to calculate
the radon flux over the studied episodes. Both goals follow into the scope
of the traceRadon project.
As described by Grossi et al. (2018) and Levin et al. (2021), it is very
important to understand how the different selections in the application of
this method will influence its result. Thus, there is a huge need to develop
and test an agreed standard procedure for application of the RTM on
different AMN sites. Such procedure would be a starting point for how the
climate community could utilise radon measurements on local and regional
scales from operational networks such as ICOS. The project traceRadon will
provide main steps in overcoming these weaknesses. The first steps in this
direction are described in section 6 and
7 by developing new sources and specifying
requirements for transfer standards. Moreover, this procedure is important
for GHG emission estimates that support national reporting under the Paris
agreement on climate change.
Radon in Radiation Protection
The Council Directive 2013/59/EURATOM, published in 2014, contains new
requirements for radon protection. Article 103 (3) requires Member States to
identify areas where the radon activity concentration (annual mean) is
expected to exceed the relevant national reference value in a significant
number of buildings. In these areas, Member States are requested to
establish programmes to carry out radon measurements in workplaces that are
located at ground or basement level (Article 54 (2)). The establishment of
Radon Priority Areas (RPA) is therefore an important step in the
implementation of the Directive and in the radon action plans of the Member
States.
Maps directly or indirectly related to soil 226Ra content existed in
many member countries long before the implementation of the European
Directive (Dubois, 2005). They are an important part of national
radon strategies as a tool for prioritization of radon protection measures
(e.g., structural precautions, radon measurements, awareness campaigns for
decision makers and the public). Radon maps and RPAs can be produced and
displayed using very different methods, depending on the intended use of the
map and the available data (Bossew, 2018). Many maps and the setting of RPAs
are based on indoor radon measurements in residential buildings, sometimes
linked to information on building characteristics (e.g., Austria, see
Friedmann, 2005). Other countries base the determination on data on radon
in soil gas (e.g., Czech Republic and Germany, see Neznal et al., 2004 and
Kemski et al., 2001) respectively. Another method for characterizing an area
in terms of its radon potential is to link different radon-relevant
parameters (e.g., radon in soil air, soil permeability, concentration of
radionuclides in soil, soil characteristics). This is often referred to as
the geogenic radon potential, and methods for this have been further
developed thanks to the MetroRADON project (e.g., the Radon Hazard Index,
RHI) (Bossew et al., 2020).
The Joint Research Centre of the European Commission (EC-JRC) has been
collecting data on radon and natural sources of radiation from European
countries and from available European databases. As results, the European
Atlas of Natural Radiation (Tollefsen et al., 2019) contains a collection of maps showing
the levels of natural sources of radiation in different parts of Europe.
Moreover, it provides reference values for natural sources of radiation
across Europe and makes harmonised datasets available to the scientific
community and national authorities. This also serves the purpose of raising
awareness about natural radioactivity in the public. The Atlas publication
is available in digital format and as a printed version, in addition an
online version is regularly updated when new data is available
(https://remon.jrc.ec.europa.eu, last access: 2 March 2022). Radon outdoor air
and radon flux maps have not been developed in the Atlas project so far,
because the data were not yet available, and especially not robust and
comparable. In the traceRadon project, for the first time an evaluation
whether and how these data can be used in future methods and models for
radon mapping and determination of RPAs is performed. Consideration of
dynamic soil parameters (e.g., soil moisture) on radon transport processes,
and thus on radon activity concentrations in soil air, may contribute
significantly to characterization of radon potential. Within this project
experimental calibrated data of atmospheric radon activity concentrations
and radon flux as well as dose rate and spectrometry data (Röttger
and Kessler, 2019) will be used to validate available radon flux models and
inventories (e.g., Szegvary et al., 2009; Karstens et al., 2015). Finally,
it is planned to make the radon outdoor air monitoring stations available
online similar to the local gamma dose rate via EURDEP.
New activity standards
To start the development of new sources for the calibration needs (Linzmaier
and Röttger, 2014), a literature study of currently available radon sources for
the calibration of instruments capable of measuring radon activity
concentrations below 100 Bq m-3 was performed. Environmental
parameter ranges were evaluated and a suitability list for in-field
calibration was defined. That led to new needs for these characteristics,
specifically the ability to produce reference atmospheres at the ambient
levels as well as high stability concerning environmental parameters for
potential in-situ applications. Currently, no sources which meet both
criteria are available and so alternative sources had to be developed for
the traceRadon Project: low activity emanation sources. Two different
principles were applied:
a radon emanation source is created from an emulsion of salts of fatty acids
in silicone rubber, formed from a weighed standard solution of 226Ra.
Traceability of the 226Ra activity is established by weighing and
γ-spectrometry: Using a stainless-steel cylindrical case with valves
and aerosol filters, applying ultra-dried air and a mass flow controller
with additional humidifier, to control the dilution of the activity
concentration, a time-stable radon activity concentration is achieved. This
principal was already successfully applied in MetroRADON (Fialova et al.,
2020);
a new development is the low-level, low activity emanation sources based on
the electrodeposition from a carrier-free 226Ra solution on a
stainless-steel plate. For futher information on this source design, the
reader is directed to Mertes et al. (2020). The emanation rate of 222Rn
of these sources is followed online via γ-spectrometry using
portable scintillation detectors like LaBr3-Crystals.
Due to conservation of the amount of substance, the 222Rn activity
retained within in an emanation source must balance the ingrowth, decay and
release of 222Rn nuclei. Based on this observation, the measurement of
residual 222Rn yields the emanation convolved with a certain impulse
response characteristic that directly results from the well-known
radioactive decay kinetics. Consequently, the γ-ray spectrometric
measurement of the disequilibrium between 226Ra and the residual
222Rn decay products allows to directly calculate the emanation only
once a stable state has been reached. During in-field calibrations, however,
the environmental conditions are expected to change, which can change the
emanation characteristics. To overcome this constraint, an algorithm
implementing a technique of statistical inversion based on recursive
Bayesian estimation has been developed and implemented (Mertes et al.,
2021). Using this algorithm, the probability density function of the
estimated emanation of 222Rn in terms of atoms per unit time is
estimated using the supporting γ-ray spectrometric measurements. The
recursive construction of the algorithm allows to best use the previously
observed γ-ray spectra to determine the emanating amount in near
real time, limited by the statistical uncertainty that can be achieved
during the integration time of the spectrometer. As an input to the
algorithm, the integral count-rate of a γ-ray spectrometer above
200 keV is used. A typical result of the application of this algorithm
together with the input data is given in
Fig. 1, which shows distinct behaviour of
the inferred emanation resulting from changes in the relative humidity.
Analogous behaviour is expected concerning changes in the ambient
temperature and possibly pressure. Despite these environmental influences,
different techniques of calibration can be realized based on the inference
of a continuous 222Rn source term.
The first (upper) diagram shows the integral count rate above the
highest energy of 226Ra of an electrodeposited source, which is the
input data to the algorithm. The variation of this count rate is achieved by
variation of environmental parameters, specifically, the relative humidity.
The second diagram presents the remaining 222Rn activity in the source,
given in Bq, inferred from the count rate data. The light blue area
represents the 90 % confidence interval for the uncertainty of the
measurements. The third diagram gives the primary desired result, which is
the emanated number of 222Rn atoms, represented as atoms s-1. Upon
changes in the emanation, the confidence intervals increase, since the
inference can then only be carried out using few data points. Within stable
regimes, as time goes on, more data becomes available, such that the
confidence intervals continually shrink.
In the scope of traceRadon, the two different sources will be compared
regarding their applicability for in-situ calibrations, their stability with
respect to environmental parameters as well as the match between their
indicated 222Rn emanation values. Note, that the line of traceability
for the two sources is very different: (1) Achieves traceability to the SI by
the traceability of the weighing process and is thus traceable to the
national 226Ra standards of the CMI (Fialova et al., 2020) and by
characterization of the emanation by γ-ray spectrometry in
comparison to simulated results. On the other hand, (2) achieves primary
definition of the 226Ra activity, traceable to the meter and the second
by employing defined solid-angle α-particle spectrometry and
characterizes the emanation by γ-ray spectrometry in comparison with
a sealed reference source (Mertes et al., 2020). While the stability with
respect to environmental changes is assumed for source type (1), it can be at
least retrospectively monitored for source type (2) using the outlined
algorithm. Therefore, consistent calibration results with each source will
provide significant confidence concerning the correctness of the applied
methods. This may only be achieved by pursuing different source construction
techniques with independent traceability chains.
Radon monitors – An overview
With the new sources traceable calibrations are feasible, but as a
prerequisite an instrument capable to operate in that range of activity
concentration is needed. Nowadays a variety of commercial radon monitors are
available on the market based on different measurement techniques.
Additionally, radon monitors have also been developed at some research
institutes. A literature review of the currently available continuous radon
monitors capable of measuring activity concentrations below
100 Bq m-3 was carrying out during the first months of the
traceRadon project. A summary of it is reported in Table 1 with the main
characteristics of the monitors as declared by the manufacturer. Often the
trade-off between commercial and research-grade radon monitors is a
reduction of portability for an increase in accuracy at low-level
measurements. Note that the nominal sensitivity in
Table 1 is the one declared by the manufacturers and
it is considering only the uncertainty of the total counts in the region of
interest of each instrument for radon measurement and/or calculation. This
information only gives a first order of magnitude to compare the different
monitors but other factors influencing the total uncertainty of the
measurement such as calibration factor uncertainty, background uncertainty,
interference factor uncertainty, uncertainties of correction factors applied
to the different monitors due to their measurement method (temperature,
water content, pressure, time response, deconvolution, etc.) are not taken
into account (Radulescu et al., 2022). In addition, a desired matrix of
properties usable for radon activity concentration monitors for use as a
transfer standard in the field are shown in Table 2.
They also provide a mark to be accomplish for atmospheric radon measurements
at AMN from the point of view of the traceRadon project. The matrix is
available to guide developers and producers in instrumental design for
climate observation networks, since currently no IEC standard for this
application exists.
Main technical characteristics of radon and radon progeny monitors.
Model /manufacturerMethodSampling Flow Rate (L min-1)Nominal Sensitivity(counts per 60 s perBq m-3)Portability considerations Dimensions (cm ⋅ cm ⋅ cm) and weight (kg)Additional specificationsReferencesRAD7 /Durridge Company Inc.Electrostatic deposition10.0067 (218Po)0.013 (214Po)29.5 ⋅ 21.5 ⋅ 27.9 cm3 4.5 kg– Remote control – Power supply and battery – Need of dry airDURRIDGE Company Inc. (2021)RTM 2200 /SARAD GmbHElectrostatic deposition0.60.003 (218Po)0.007 (214Po)23.5 ⋅ 14.0 ⋅ 25.5 cm3 6 kg– Radon concentration fast (excl. Po-214,12 min) and slow (incl. Po-214, 120 min)Streil et al. (2011), SARAD GmbH (2022)RADIM 3AT /TeslaElectrostatic deposition–0.0083 (218Po)23 ⋅ 23 ⋅ 23 cm3 1.5 kg– Only works on diffusivity modeTesla (2018)AlphaGUARD /Bertin Instruments –SaphymoPulse ionization chamber10.0532.9 ⋅ 35.5 ⋅ 12.3 cm3 6.2 kg– Fast transient response – Automatic background correctionRoessler (2020)ATMOS /Radonova Laboratories ABPulse ionization chamber10.0250 ⋅ 38.5 ⋅ 22 cm3 4.5 kgMazed et al. (2007)Pylon AB7 /Pylon Electronics Inc.Lucas scintillation cells0–2.50.03731 ⋅ 23 ⋅ 20 cm3 5 kg– Continuous Monitoring / – Grab SamplingSouthern Scientific (2022)MiAm MR1 /Mi.am SrlScintillation celldiffusion0.0439 ⋅ 19 ⋅ 11 cm3 4.5 kgCardellini et al. (2013), Cardellini (2017)ANSTO / Australian Nuclear Science and Technology OrganisationDual-flow-looptwo-filter– Remote control – Time response correctionWhittlestone and Zahorowski (1998) Brunke et al. (2002) Chambers et al. (2018) Grossi et al. (2020)1500 L80–10021300 ⋅ 80 ⋅ 80 cm3 120–140 kg700 L40–6010260 ⋅ 60 ⋅ 60 cm3 80–90 kg200 L12–153150 ⋅ 48 ⋅ 48 cm3 35–45 kgARMON 20 L /Institut de TècniquesEnergètiques (INTE) –Universitat Politècnica deCatalunya (UPC)Electrostatic deposition1.5–2.00.3990 ⋅ 80 ⋅ 80 cm3∼ 10 kg– Remote control – Need of dry air simpleGrossi et al. (2012) Vargas et al. (2015), Grossi et al. (2020)HRM /HeidelbergUniversityOne-filter∼ 202035 ⋅ 30 ⋅ 15 cm3∼ 8 kg– 214Po measurement – Remote control – Sampling inlet height correctionLevin et al. (2002)LSCE /Laboratoire desSciences du Climat et del'Environnement (LSCE)One-filter∼ 16025 ⋅ 25 ⋅ 40 cm3∼ 8 kg– α-Spectrum – Remote control – Sampling inlet height correction – Need of large pumpPolian et al. (1986) Biraud et al. (2000)Radon Mapper /Mi.am SrlLucas scintillation celldiffusion0.0439 ⋅ 39 ⋅ 11 cm3 4.5 kg– Integrated WiFi (full remote control) for measurement campaignsMi.am Srl/Tecnavia SA – RadonDetectors (2019)BWLM PLUS 2S RadonDaughter /Tracerlab Engineering &TechnologySi surface barrier detector1000.04 (α Po-218) 10.6 (α Po-214)32.5 ⋅ 25.5 ⋅ 15.5 cm3 9.0 kg– Continuous-Method to select independentcounting-intervals – Nuclide-Specific-Calculation Method in fixed intervals of one hour, for the determination of single nuclides of the Radon/Thoron-Daughter concentration – Runtime without AC-line connection to the charger >10 hCardellini (2017)
Matrix of recommended properties for the in-field application of a
transfer standard radon monitor for atmospheric measurements.
PropertyRecommended range for in field applicabilityEnvironmental temperature T (∘C)-25 to +50∘CEnvironmental relative humidity rH (%)10 % to 100 %Atmospheric pressure p (hPa)620 to 1030 hPaMeasurable atmospheric radon activity concentration cA (Bq m-3)1 to 200 Bq m-3Sensitivity k (counts per 60 s per Bq m-3)>0.3 (60 s Bq m-3)-1Total uncertainty u (%) for activity higher than 0 Bq m-3 and less than 100 Bq m-3 within 1 h (k=2)<20 %Detection Volume V (m3) and<1 m3weight G (kg)<70 kgOutlook
Atmospheric measurements of radon activity concentrations can become a
pillar in the assessment and improvement of ATM. For this aim, the metrology
of the radon activity concentration has been improved by the development of
a new traceability chain in extension of Pierre et al. (2021), a new data
analysis for the online source application and by the implementation of a
matrix with recommended properties for the in-field application of a
transfer standard radon monitor for atmospheric measurements.
This is also the first step to overcome the current weaknesses in the RTM.
The next step within traceRadon will be to establish a traceability chain
for radon flux measurements as well.
Useable dynamic radon activity concentration and radon flux maps will be
provided through the Radioactive Environmental Monitoring web portal (REMon,
https://remon.jrc.ec.europa.eu, last access: 2 March 2022)
operated by the Joint Research Centre of the European Commission and through
the ICOS Carbon Portal. This new data will be linked to already established
data from EURDEP (European Radiological Data Exchange Platform) and EANR
(European Atlas of Natural Radiation) and will be made available to
scientists, policy makers and end users. Concerning radiation protection,
the focus is on the improvement of methods for the identification of Radon
Priority Areas and the identification of radon wash-out peaks from total
gamma dose rate data.
Data availability
The authors confirm that the data supporting the findings of this
publication are available in the references given or in case of the
emanation sources on the SharePoint of the tracRadon Project (https://npluk.sharepoint.com/sites/traceRadon, last access: 2 March 2022). Additional
data on the emanation sources is available from the corresponding author
upon reasonable request.
Author contributions
SR form PTB drafted the outline of the manuscript with contributions from
all co-authors. The text was prepared by him and edited jointly (SR, AR, CG, AV, UK, GC, EC, DK, CR, FM, IR). All
co-authors provided significant input according to their expertise,
especially: SR is responsible for WP1, CG for WP2, UK manages WP3, GC
handles WP4, AR is managing WP6, while the WP5 is in the responsibility of
CR.
Competing interests
The contact author has declared that neither they nor their co-authors have any competing interests.
Disclaimer
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Special issue statement
This article is part of the special issue “Geoscience applications of environmental radioactivity (EGU21 GI6.2 session)”. It is a result of the EGU General Assembly 2021, 19–30 April 2021.
Acknowledgements
EMPIR 19ENV01 traceRadon started to run in summer 2020. It is supported by a
broad global scientific community within atmospheric and climate research,
radiation protection and metrology. All stakeholders are united by the goal
of providing new and improved data and maps for science, the public and
decision makers. The early results are coming from the design and building
of new technologies for calibrating high-sensitivity atmospheric radon
monitors. The consortium would like to thank the staff of project partners
and collaborators of traceRadon, as well as all institutions and
organisations that supported the project with recommendations. In the
preparation of the project, the communication and discussion within EURADOS
WG3 turned out to be very effective. Further thanks go to EURAMET e.V., the
European Association of National Metrology Institutes which made such a
project possible within the EMPIR framework program. For the time being, the
project traceRadon has established the following collaborations by a Letter
of Agreement (in the order of signature date):
(1)
Universität Heidelberg, Germany. (2) ANSTO, Australia's Nuclear Science and Technology Organisation, Australia. (3) ERA, European Radon Association, Europe. (4) Met Office, United Kingdom. (5) University of Novi Sad, Serbia. (6) Politecnico di Milano, Italy. (7) University of Cordoba, Spain. (8) EURADOS, e.V., Europe. (9) Universität Siegen, Germany. (10) IRSN, France. (11) ARPA Piemonte, Italy. (12) ARPA Valle d'Aosta, Italy.
The consortium is grateful to have this powerful support from colleagues
worldwide. Further collaboration interest is welcome.
This project traceRadon has received funding from the EMPIR programme
co-financed by the Participating States and from the European Union's
Horizon 2020 research and innovation programme. 19ENV01 traceRadon denotes
the EMPIR project reference.
Financial support
This project 19NET01 traceRadon has received funding from the EMPIR
programme co-financed by the Participating States and from the European
Union's Horizon 2020 research and innovation programme. 19NET01 traceRadon
denotes the EMPIR project reference.This open-access publication was funded by the Physikalisch-Technische Bundesanstalt.
Review statement
This paper was edited by Virginia Strati and reviewed by Alastair Williams and Xuemeng Chen.